Palantir Ontology, Explained

Palantir's own architecture docs state its Ontology is not a semantic layer, and its 2025 10-K says the Ontology goes far beyond the ordinary meaning of that word — yet Palantir's documents split the Ontology into two, three, four, or six parts, depending on the page.

Palantir's documentation defines an action as a single transaction, then draws that transaction's boundary narrower than the word suggests: object edits and one writeback webhook sit inside it, while every notification and side-effect webhook runs outside, asynchronously, best-effort.

In August 2024, a Palantir forum user asked for a code-based way to define the Ontology; an employee said the tooling was not ready. This piece checks how much of four lenses — semantic definition, action, permission, lineage — a contract, a test, and an approval list in three public repos cover, and which slices are not the same thing as Palantir's.